Metal strut for aircraft



H. N. WYLIE.

METAL STRUT FOR AIRCRAFT.

APPLlCATlON FILED AUG.22. 1919.

Patented Jan. 4, 1921.

F/aJ.

I 0 n I 0 0 a 00 PATENT OFFICE.

UNITED STATES HAMILTON NEIL WYLIE, OF EDINBURGH, SCOTLAND.

METAL STRUT FOR AIRCRAFT.

T 0 all whom it may concern Be it known that I, HAMILTON NEIL 'WYLIE,major in the Royal Air Force, a subj ect of the Kin of Great Britain,residing at 16 Comiston Brive, Edinburgh, Scotland, have inventedcertain new and useful Im provements in Metal Struts for Aircraft, ofwhich the following is a specification.

This invention relates to aircraft members that are made from thin metaland that are subjected mainly to thrust.

The invention consists in designing such members so that the applicationof the load on a member causes the member as a whole, or causes itscomponent parts to bend in a predetermined manner such that its lessrigid parts are subjected to relatlvely light compression stress or totenslon stress.

By this arrangement the stresses can be localized on the parts of themember best able to withstand them, and the edges along which theplates, strips, or bars, forming the member, are connected together, orthe parts of them that are only slightly curved in the cross-section ofthe member are relatively lightly stressed.

By this arrangement also any bracing members which may be used in theconstruction of the member may be adapted to resist tension only.

The invention is illustrated in the drawings accompanying thisspecification, in which Figure l is a cross-section of a streamlinestrut, Fig. 2 shows the same strut in elevation, and Fig. 3 shows amodified form of strut. in elevation.

Referring now to the drawings, the inven tion is shown in itsapplication to interplane struts and other struts in the wind stream, inFigs. 1 and 2, in which A is a thin plate bent with relatively greatcurvature at B to form the leading portion of the strut, which is ofstreamline cross-section, and

therefore only slightly curved on the side portions at C. D is a web ofchannel cross section connected through packing strips M to the plate Aby any ordinary means. \Vith the cross-section shown, the plate at B isenabled by its curvature to develop higher compression stress withoutbuckling than at C, where the plate is almost fiat and where the edgesoccur.

According to the invention, the load is applied along an axis through Lwhich lies be- Specification of Letters Patent.

Patented Jan. 4., 1921.

Application filed August 22, 1919. Serial No. 319,244.

tween the centroid G of the metal in the cross-section and the leadingedge B. The ends of the strut will be suitably designed in accordancewith the usual practice for the load to be effectively applied at theends of the axis through L. The method of forming the ends of the strut65 this purpose, however, forms no part of the invention.

The centroid G is determined for that part of the complete cross-sectionof the strut which functions in resisting stresses. For example, in Fig.3 the fairing (not shown in the drawing which may be applied to completethe strut may be of such light and nonresistant material, such as papiermach, that it adds no appreciable strength, and in this case thecentroid G is that of the sheet metal portion of the strut only.

In Figs. 1 and 2 are shown a form of cross-section of strut whichcomprises a fore part of sheet steel A anda rear part N which may be oflighter material such as aluminium, the two parts A and N beingconnected together as shown. The fore part A contains a packing piece Mand within the said packing piece a web of channel cross-section D isattached. Owing to the projecting edges of the fore part A and the webof the channel D a groove is left into which the leading edge of thefairing N is received and positioned. Formers O at suitable distancesapart are attached to the channel D and fore part A by a looking pin P,andthe fairing N is riveted to these formers which retain the fairing inposition. The fairing N is anchored at each end of the strut by anyattachment preventing longitudinal movement relatively to the fore partA and as illustrated by means of a shoe R. In the case of struts of thisand similar forms, the area of an element of the cross-section ismultiplied by the elastic constant of that element in determining thecentroid G of the cross-section. The load will then be applied to thestrut along an axis which is in front of the centroid.

In the form of construction shown in Fig. 3 stiffness is givengi-to thestrut about the transverse axis of the cross-section by a tension memberE attached at its ends to the top and bottom of the strut and held awayfrom the web of the strut at intervals in its length by truss pieces F.By placing the axis of loading near to the leading edge B ashereinbefore described, the member E is subjected to tension by theapplication of load to the strut. v

Vhen the strut is relatively flexible about its transverse axis, it hasbeen found advantageous to make the truss pieces F stiif and to connectthem rigidly to the strut and also to connect the tension member E tothe truss pieces. By this means, the lengths of strut between adjacenttruss pieces have their ends fixed in direction by the truss pieces andare thus enabled to carry a much hi her load.

5V hen this strut Fig. 3 is used in the wind stream and provided with afairing as illustrated in Figs. 1 and 2, the tension member couldsuitably form a support for the trailing edge of the fairing.

It has been found advantageous in many cases to form the fairing ofstruts from thin aluminium sheet. This sheet, however, is liable tobuckle and wrinkle .when the strut is shortened by the application ofthe load. By causing the strut to bend slightly with its leading edge incompression in accordance with my invention the rear part of the fairingis relieved of its compression stress and even put in tension, but theportions of the fairing adjacent to the strut proper are liable to-bestill in compression. To prevent these portions from buckling in anirregular manner, it has been found advantageous to form fore-and-aftflutings K in these parts of the fairing.

This arrangement is shown in Fig. 2. N is the fairing composed of thinaluminium sheet. The portions of the fairing extending from the web D tothe lines XX are incompression and are formed with flutes K, while theportion H of the fairing at the rear of the lines XX is in tension owingto the bending action of the strut.

Most of the members hereinbefore described are suitable for other thanaircraft structures. They are particularly suitable for structures inwhich lightness is essential, such as long span conveying andtransporting structures. It is to be understood that the scope of theinvention is not limited to members for aircraft.

What I claim as my invention and desire I to secure by Letters Patentis 1. An aircraft strut comprising in combination a thin metal stripbent upon itself in the direction of its length with a relatively greatcurvature to compose the forward portion of a streamline body the rearedges of said strip being at a distance apart, a

web of thin sheet metal located between and connecting the said rearedges of said bent forward part, means for fixing said edges of said webto said rear edges of said forward part and a stress resisting memberconnected to said rear edges of said forward bent part to form thetrailing part of the structure, said strut structure being adapted forthe application of the load in a plane parallel to the centroid axis ofthe strut and between said axis and the leading part of said bentforward part.

2. An aircraft strut comprising in combination a thin metal strip bentupon itself in the direction of its length with a relatively greatcurvature to compose the forward portion of a streamline body, the rearedges of said strip being at a distance apart, a web of thin sheet metallocated between and connecting the said rear ed es of said bent forwardpart, means for fixing said edges of said web to said rear edges of saidforward part, a stress resisting member comprising a strip of sheetmaterial bent longitudinally upon itself to form a fairing to composethe trailing part of the structure, means for attaching the forwardedges of said fairing to the rearward edges of said bent forward partand means for connecting said fairing to said bent forward part at eachend of the strut to prevent longitudinal movement of said fairingrelatively to said bent forward portion, said strut structure beingadapted for the application of the load in a plane parallel to thecentroid axis of the strut and between said axis and the leading part ofsaid bent forward part.

3. An aircraft strut comprising in combination a thin metal strip bentupon itself in the direction of its length with a relatively greatcurvature to compose the forward portion of a streamline body, the rearedges of said strip being at a distance apart, a web of thin sheet metallocated between and connecting the said rear edges of said bent forwardpart, means for fixing said edges of said Web to said rear edges of saidforward part, a strip of thin sheet metal such as aluminum bentlongitudinally upon itself to form a fairing to compose the trailingpart of the structure, the relatively slightly curved forwardlyextending sides of the fairing having flutings spaced apart andextending in a forward and rearward direction to prevent said side partsof the fairing from buckling in an irregular manner, means for attachingthe forward edges of the fairing to the rearward edges of the bentforward part and means for connecting said fairing to said bent forwardpart at each end of the strut to prevent longitudinal movement of thefairing relatively to said bent forward part, said strut being adaptedfor the application of the load in a plane parallel to the centroid axisof the strut and between said axis and the leading part of the said bentforward part.

4. An aircraft strut comprising in combi nation a thin metal strip bentupon itself in the direction of its length with a relatively greatcurvature to compose the forward portion of a streamline body, the rearedges of a forward bent portion to form/the trailing part of thestructure, said strut structure being adapted for the application of theload in a plane parallel to the centroid axis of the strut and betweensaid axis and the leading part of said bent forward part.

5. An aircraft strut comprislng in combnation a thin metal strip bentupon itself in the direction of its length with a relatively greatcurvature to compose the forward portion of a streamline body, the rearedges of said strip being at a distance apart, packing strips one oneach inner surface of the side members of the bent forward part and nearthe rear edges thereof, a web of thin sheet metal of channel sectionhaving its flanges extending rearwardly and located between the rearedges of said bent forward part in contact with said packing strips andextending rearward of same to form rooves between the rear edges of saidbent orward part and the rear edges of said flan es of saidchannel'section web, means for xing the flanges of said channel sectionweb and said pac ing strips to the interior facing surfaces of said bentforward part, a strip of thinsheet metal bent longitudi nally uponitself to form a fairing to compose the trailin part of the structure,the relatively sli ht y curved forward edges of said fairing tting intosaid grooves of said bent forward part, means for fixing the forwardedges of said rearward fairing to said bent forward part, shoes forconnecting said fairing to said bent forward part at each end of thestrut to prevent longitudinal movement of said fairing relatively tosaid bent forward part and means for applying the load to the strutstructure in a plane parallel to the centroid axis of the strut andbetween said axis and the leading part of said bent forward part.

In Witness whereof I have hereunto set my hand in the presence of twowitnesses.

HAMILTON NEIL WYLIE.

